1. Field of the Invention:
The present invention relates generally to well production equipment, and in particular, to apparatus for inserting and withdrawing flexible production tubing into and out of a well.
2. Description of the Prior Art:
Submersible pumps of the type in which the pumping force is derived from electrical, hydraulic, or pneumatic power applied downhole represent a significant improvement over the reciprocating sucker rod approach. According to conventional practice, a submersible pump which is driven downhole by electrical, hydraulic or pneumatic driving means is supported at the end of a long string of steel tubing joints which are coupled to each other by pin-and-box threaded connections. Power conductors, signal conductors and hydraulic/pneumatic conduits coupled to the downhole pump are bundled together within an external umbilical cable assembly and are secured to the rigid production tubing joints.
Although large diameter steel production tubing has great strength and durability, it requires a substantial capital investment. The procedure of running rigid sections of production tubing into and out of the well bore is complicated by the external umbilical cable assembly. Moreover, the steel production tubing, as well as the pump, is subject to corrosion so that it may be necessary to pull the production tubing from the casing and repair the pump or replace damaged production tubing sections from time to time. When such workover operations become necessary, a portable installation called a workover rig must be brought to the well site and set up. Generally, these rigs consist of a heavy derrick or mast which support block and tackle draw works for pulling the pipe string from the well. The workover rigs are usually heavy and difficult to erect and must be capable of lifting the substantial load imposed by the rigid pipe string.
An overriding concern in the operation of a producing well is to get the necessary equipment into and out of the well as rapidly as is economically possible. The efficiency of the pipe-handling operation is limited by such factors as the running speed of the hoist rig, the time required to make up or break tool joints during stabbing operations, the time required to mechanically couple and decouple the hoist rig and the pipe string, and the time required to transport lengths of pipe from the well head to a storage station during recovery operations and to transport lengths of pipe from the storage station to the well head during launching operations. As the length of the pipe string increases to reach the producing formation of deep wells, the pipe handling equipment must safly support the large load of the pipe string and permit the efficient execution of launching and recovery operations while preserving the structural integrity of the pipe string during the handling operations.
It will be appreciated that the substantial capital expenditure required for large diameter steel production tubing, and the expense associated with deployment, recovery and repair or replacement of the rigid production tubing make its use prohibitive in low production wells, and account for a substantial percentage of the overall production costs of other wells.
For the foregoing reasons, there is considerable interest in improving production systems in which the rigid production tubing is replaced by less expensive flexible production tubing which is relatively easy to deploy and recover. Examples of production systems which utilize flexible production tubing are disclosed in U.S. Pat. Nos. 4,336,415 and 4,345,784, both by John B. Walling.